1. Field of the Invention
The invention relates to a process for the preparation of organic acids from, for example, Fermentatively prepared salt solutions. Through the use of electrodialysis it is possible to extract the free organic acids and simultaneously to provide the starting substance for the fermentation.
2. Discussion of the Background
For the fermentative conversion of, for example, fumaric acid to L-malic acid, bacteria (German Pat. No. 2,363,285), immobilized bacteria (Europ. J. Appl. Microbiol. 3, 169 (1976)), fungi (German OS 3,310,849), or even immobilized fungi (German OS 2,415,310) may be used. L-malic acid may also be prepared from glucose by means of fungi and bacteria (J. Ferment. Technol. 54, 197 (1976)).
The method of electrodialysis is used in the processing of fermentatively prepared organic acids as early as the fermentation or at a later stage. The objective may be to purify the product or to separate various products from each other or the conversion of the product obtained as a salt into the free acid. The known processes relate to itaconic acid (U.S. Pat. No. 3,873,425), lactic acid (German OS 1,957,395), gluconic acid and glutamic acid. In the process for the preparation of itaconic acid, electrodialysis achieves only a starting-material/product separation and further steps employing ion exchangers are necessary.
Various processes are described for the separation of, for example, L-malic acid from the reaction mixture. Thus, it is proposed to precipitate L-malic acid as the calcium salt (German OS 1,417,033). Fumaric acid is also precipitated at the same time. In this process, losses of materials are unavoidable in the separation of the fumaric acid. Calcium compounds are also needed in this process. A treatment with ion exchangers to convert the salt into the free L-malic acid is also described (German OS 3,247,981). During the regeneration of the ion exchanger, losses of substance inevitably occur. After the regeneration, the eluate represents an environmental pollutant. The use of an additional acid for the regeneration is unavoidable.
By electrodialysis it is also possible to convert a salt of an organic acid (BY) into the free acid (H.sub.2 Y) using another acid (H.sub.2 X). EQU BY+H.sub.2 X.fwdarw.H.sub.2 Y+BX
In this process a salt (BX) is produced which must be disposed of. The known processes for the processing have the following features:
(1) several process steps (filtering, washing out, dialysis, making up of new solution), PA1 (2) consumption of extraneous substances (calcium salt, acids), and PA1 (3) issue of superfluous streams (wash water, eluates).